1. Field of the Invention
The invention relates to transparent and in particular glass substrates covered with a stack of thin layers incorporating at least one metal layer able to reflect solar radiation and/or infrared radiation of considerable wavelength.
The invention also relates to the use of such substrates for the manufacture of solar protection or control and/or thermal insulation glazings. These glazings are used both for equipping buildings and vehicles, with a particular aim of reducing air conditioning requirements and/or reducing excessive overheating resulting from the ever-increasing size of the glazed surfaces in car bodies.
2. Discussion of the Background
A known layer stack type for giving solar protective properties to substrates is constituted by at least one metal layer, such as a silver layer, which is placed between two dielectric material layers of the metal oxide type. This stack is generally obtained by a succession of deposits carried out by a method using a vacuum such as magnetic field-assisted cathodic sputtering.
Thus, patent application WO 90/02653 discloses a laminated glazing intended for cars and whose outermost glass substrate with respect to the vehicle body is provided with a stack of five layers on its inner face in contact with the thermoplastic material interlayer. This stack consists of two silver layers intercalated with three zinc oxide layers, the silver layer closest to the outer substrate carrying the stack having a thickness slightly exceeding that of the second silver layer.
The laminated glazings according to said application are used as windscreens, which explains why they have very high light transmission values T.sub.L of approximately 75%, in order to meet the safety standards in force and therefore have a relatively high solar factor value SF. (It is pointed out that the solar factor of a glazing is the ratio between the total energy entering the room through said glazing and the incident solar energy).
The object of the invention is to develop a transparent substrate carrying a stack of thin layers having two layers which reflect radiation in the infrared and which are more particularly of a metallic type, so that they have a high selectivity, i.e. the highest possible T.sub.L /SF ratio for a given value of T.sub.L, while ensuring that said substrate has an aesthetically satisfactory visual appearance in reflection.